<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

</head>
<body>

<script >
   let value = new Set();

   value.add('11')
    console.log(value)
   //如果没有他自己写一个
   _Set = (function () {
       function Set() {
           this.set = Object.create(null);
       }

       Set.prototype.has = function has(key) {
           return this.set[key] === true
       };
       Set.prototype.add = function add(key) {
           this.set[key] = true;
       };
       Set.prototype.clear = function clear() {
           this.set = Object.create(null);
       };

       return Set;
   }());

   let _value = new _Set();

   _value.add('11')
   console.log(_value)
</script>

</body>
</html>